An Analysis of Nonlocal Scalar Transport in the Convective Boundary Layer Using the Green's Function

Fujihiro Hamba Institute of Industrial Science, University of Tokyo, Tokyo, Japan

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Abstract

The Green's function for scalar fluctuations is introduced into a large eddy simulation of the convective boundary layer to investigate nonlocal scalar transport. This Green's function is used to derive a nonlocal expression for the scalar flux and to evaluate a coefficient called the turbulent diffusivity function. Such an expression.shows that scalar transport is nonlocal in both spce and time. It is shown that the scalar flux in the middle of the boundary layer is influenced by the scalar gradient in the whole boundary layer. The top-down and bottom-up diffusion as well as the countegradient transport is explained by the turbulent diffusivity function. Moreover, a nonlocal expression for the pressure scalar correlation term in the second-order model is proposed using the same Green's function. It is shown that the nonlocal property of the pressure term accounts for the difference in the return-to-isotropy timescales between the top-down and bottom-up diffusion.

Abstract

The Green's function for scalar fluctuations is introduced into a large eddy simulation of the convective boundary layer to investigate nonlocal scalar transport. This Green's function is used to derive a nonlocal expression for the scalar flux and to evaluate a coefficient called the turbulent diffusivity function. Such an expression.shows that scalar transport is nonlocal in both spce and time. It is shown that the scalar flux in the middle of the boundary layer is influenced by the scalar gradient in the whole boundary layer. The top-down and bottom-up diffusion as well as the countegradient transport is explained by the turbulent diffusivity function. Moreover, a nonlocal expression for the pressure scalar correlation term in the second-order model is proposed using the same Green's function. It is shown that the nonlocal property of the pressure term accounts for the difference in the return-to-isotropy timescales between the top-down and bottom-up diffusion.

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